Basic Linux comds -MIT.pdf

7/30/2019 Basic Linux comds -MIT.pdf

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Basic Linux Commands

Srihari Kalgi

M.Tech, CSE (KReSIT),IIT Bombay

May 5, 2009
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General Purpose utilities

Linux File System

File Handling Commands

Compressing and Archiving Files

Simple Filters
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Linux File System



Simple Filters
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Calender

cal: Command to see calender for any specific month or acomplete year cal [ [month] year]

$ cal april 2009

April 2009Su Mo Tu We Th Fr Sa

1 2 3 4

5 6 7 8 9 10 11

12 13 14 15 16 17 18

19 20 21 22 23 24 2526 27 28 29 30
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date

date: displays the current date

$ date

Tue Apr 21 21:33:49 IST 2009

kuteer$ date +"%D %H:%M:%S"

04/21/09 21:35:02 Options:

d - The da of the month (1-31) y - The last two digits of the year H,M,S - Hour Minute and second respectively D - the date in mm/dd/yy

For more information see man date
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echo and printf

echo: Print message on the terminal

usage: echo

$ echo "Welcome to the workshop"

Welcome to the workshop

printf: Print the formatted message on the terminal

Syntax of printf is same as C language printf statement

usage: printf


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Calculator

bc: A text based calculator

$ bc

2*10+20-9+4/2 [Input]33 [Output]

[ctrl+d] [Quit]

xcalc is graphical based calculator
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script: Record your session

script command records your session and stores it in a file

$ scriptScript started, file is typescript

$ echo "this is a sample script"

this is a sample script

$ [ctrl+d]

Script done, file is typescript

By default if you dont specify any file name the contents

will be stored in file name typescipt

$ cat typescript

Script started on Tuesday 21 April 2009 10:07:0$ echo "this is a sample script"

this is a sample script

$

Script done on Tuesday 21 April 2009 10:07:34 P
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passwd: Changing your password

passwd command allows you to change your password

kuteer:/workshop$ passwd

Changing password for srihari.

(current) UNIX password:

Enter new UNIX password:

Retype new UNIX password:

passwd: password updated successfully
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WHO: Who are the users?

who command tells you the users currently logged on to

the system

kuteer:$ who

srihari pts/0 2009-04-15 11:58 (:10.129.41.3)

nithin pts/1 2009-04-15 16:09 (:10.129.20.5)

avadhut pts/2 2009-04-13 14:39 (:10.129.45.20)

anil pts/3 2009-04-13 16:32 (:10.129.23.45)
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man - The reference Manual

man displays the documentation for a command

usage: man

ls - list directory contents

SYNOPSIS

ls [OPTION]... [FILE]...

DESCRIPTION

List information about the FILEs (th

none of -cftuvSUX nor --sort.
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Linux File System



Simple Filters
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Linux file system

Standard directory structure / - the topmost /dev - all the devices are accessible as files /var - variable data such as mails, log files, databases /usr - almost all the packages installed /etc - configuration files /home - home directories for all the users /root - home directory of the privileged user root /mnt - used to mount other directories/partitions.
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File Attributes

To see the file attributes type ls -l on your terminalkuteer:$ ls -l

$$ $$ $$

drwxr-xr-x 2 srihari srihari 144 2009-04-

-rw-r--r-- 1 srihari srihari 1548 2009-03-

drwxr-xr-x 2 srihari srihari 48 2009-03-

-rw-r--r-- 1 srihari srihari 3570 2009-03-

The file Testing.java has the following permissions -rw-rr

It has 10 characters, first character is d if its directory and -

if its file. Next 9 characters are divided into three groups with a set

of 3 characters each
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File Attributes Contd. . .

First 3 characters - Owner of the file or directory

Next 3 characters - Group

Last 3 characters - Others

r - Read i.e. File or directory is readable

w - Write i.e. File or directory is writable

x - Execute i.e. File or directory is executable

-rw-rr means it has read, write but not execute

permissions for the owner of the file, only read permissions

for the group and only read permissions for others

Fil A ib C d
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File Attributes Contd. . .

The third column of the command ls -l tells about the

owner of the file, next column tells to which group it

belongs

-rw-r--r-- 1 srihari srihari 3570 2009-03

The file Testing.java has the owner as srihari and also

belongs to a group called srihari

Ch i h Fil ib
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Changing the File attributes

chmod Changing the permissions of the file

kuteer:$ chmod o+x Testing.java

kuteer:$ ls -l Testing.java

-rw-r--r-x 1 srihari srihari 3570 2009-03-23 10:

kuteer:$ chmod 655 Testing.java


-rw-r-xr-x 1 srihari srihari 3570 2009-03-23 10:

Ch i hi


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Changing ownership

chown command is used for changing the ownership and

also group of the file

kuteer:$ chown guest Testing.java

kuteer:$ ls -l Testing.java-rw-r-xr-x 1 geust srihari 3570 2009-03-23 10:52

kuteer:$ chown guest:guest Testing.java


-rw-r-xr-x 1 geust guest 3570 2009-03-23 10:52

Fil t d
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File system commands

Deleting Files - rm

Copying and moving files - cp, mv Creating directories - mkdir

Deleting Empty Directory - rmdir

$ rm Testing.java

//deletes the file Testing.java$ cp Testing.java Copy.java

//creates the copy of Testing.java

$ mv Testing.java Test.java

//renames the file Testing.java to Test.java

$ mkdir newDir

//Creates directory newDir

$ rmdir newDir

//deletes directory newDir newDir should be emp
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Linux File System



Simple Filters

cat : Concatenate Files
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cat : Concatenate Files

cat command is used to display the contents of a small fileon terminal

usage: cat

$ cat sample3.txt

Unix (officially trademarked as UNIX, sometimes......

cat when supplied with more than one file will concatenate

the files without any header information

$ cat sample3.txt sample4.txt

/*contents of sameple3.txt*/

/*Followed by contents of sample4.txt without a

tac : concatenate files in reverse
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tac : concatenate files in reverse

tac command is used to display the contents of a small file

in reverse order on terminal

usage: tac

$ tac sample3.txt

/*displays sample3.txt in reverse order*/

tac when supplied with more than one file will concatenate

the reverse contents of files without any header information

$ tac sample3.txt sample4.txt

/*print sample3.txt in reverse order*//*print sample4.txt in reverse order without an

more less : paging output
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more, less : paging output

more and less commands are used to view large files one

page at a time

usage: more

usage: less

$ more sample1.txt

/*sample1.txt will be displayed one page

at a time */

$ less sample1.txt

/*sample1.txt will be displayed one page

at a time */ less is the standard pager for linux and in general less is

more powerful than more

wc : statistic of file
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wc : statistic of file

wc command is used to count lines, words and characters,depending on the option used.

usage: wc [options] [file name]

$ wc sample1.txt

65 2776 17333 sample1.txt

Which means sample1.txt file has 65 lines, 2776 words,

and 17333 characters

you can just print number of lines, number of words ornumber of charcters by using following options:

-l : Number of lines -w : Number of words -c : Number of characters

cmp: comparing two files
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cmp: comparing two files

cmp command is used to compare two files whether theyare identical or not

usage: cmp

The two files are compared byte by byte and the location of

the first mismatch is printed on the screen If two files are identical, then it doesnot print anything on

the screen

$ cmp sample1.txt sample2.txt

sample1.txt sample2.txt differ: byte 1, line 1

$ cmp sample1.txt sample1_copy.txt

$ /*No output prompt returns back*/

comm : what is common?
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comm : what is common?

comm command displays what is common between both

the files

usage: comm

The input files to comm command should be sorted

alphabetically

$ comm sample5.txt sample6.txt

anil

barun

dasgupta

lalit

shukla

singhvi

sumit

comm: contd
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comm: contd. . .

Column 1 gives the names which are present in

sample5.txt but not in sample6.txt

Column 2 gives the names which are not present insample5.txt but present in sample6.txt

Column 3 gives the names which are present in both the

files
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Linux File System



Simple Filters

gzip and gunzip


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gzip and gunzip gzip command is used to compress the file, and gunzip is

used to de-compress it.

usage: gzip

It provides the extension .gz and removes the original file

$ wc sample_copy.txt

65 2776 17333 sample_copy.txt

$ gzip sample_copy.txt

$ wc sample_copy.txt.gz26 155 7095 sample_copy.txt.gz

The compression ratio depends on the type, size and

nature of the file usage: gunzip

$ gunzip sample_copy.txt.gz

$ /*do ls and you can see the original file*/

If you want to compress the directory contents recursively,

use -r option with gzip command and unzip it use the

same option with gunzip command

tar : The archival program


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tar : The archival program

tar command is used to create archive that contains a

group or file or entire directory structure. It is generally used for back ups.

usage: tar [options] . . .

The following are the options: -c Create an archive -x Extract files from archive -t Display files in archive -f arch Name the archive arch

$ tar -cvf compression.tar compression

compression/ //v for verbosecompression/temp/

compression/temp/sample2.txt

compression/sample1.txt

tar contd. . .
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tar contd. . . We can use tar and gzip command in succession to

compress the tar file.

$ tar -cvf compression.tar compression$ gzip compression.tar

$ //will create compression.tar.gz file

For un-compression the file first use gunzip command,

which will create a tar file and then use tar command to

untar the contents$ gunzip compression.tar.gz

$ tar -xvf compression.tar

To just view the contents of the tar file use -t option

$ tar -tvf compression.tar$ tar -tvf compression.tar

drwxr-xr-x srihari/srihari 0 2009-04-22 11:29

drwxr-xr-x srihari/srihari 0 2009-04-22 11:29

-rw-r--r-- srihari/srihari 17663 2009-04-22 11:2

-rw-r--r-- srihari/srihari 17333 2009-04-22 11:2

tar contd. . .
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Instead of doing tar first and then gzip next, we cancombine both of them using the option -z

$ tar -cvzf compression.tar.gz compression

compression/

compression/temp/compression/temp/sample2.txt

compression/sample1.txt

We can de-compress .tar.gz agin in a single command

using the option -z with -x

$ tar -xvzf compression.tar.gz

zip and unzip: compressing and archiving
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p p p g g

zip command can be used for archiving as well as

compressing the contents of the directory or the file

usage: zip [options] output.zip

$ zip sample1.zip sample1.txt

//will create sample1.zip file Use -r option to recursively zip the contents of the directory

$ zip -r compression.zip compression

// will create compression.zip file

To un-compress the file use unzip command$ unzip compression.zip

// will uncompress the compression.zip file
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Linux File System



Simple Filters

Filters


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Filters are commands which accept data from standard

input, manupulate it and write the results to standard

output

head command displays the top of the file, when used

without any option it will display first 10 lines of the file

$ head sample1.txt

/*display first 10 lines*/

Similarly tail command displays the end of the file. Bydefault it will display last 10 lines of the file

$ tail sample1.txt

/*display last 10 lines*/

tail or head with -n followed by a number will display that

many number of lines from last and from first respectively

$ head -n 20 sample1.txt

/* will display first 20 lines*/

$ tail -n 15 sample1.txt

/* will display last 15 lines */

cut : cutting columns


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cut command can be used to cut the columns from a file

with -c option

usage: cut -c [numbers delemited by comma or range]

$ cut -c 1,2,3-5 students.txt

1 ani

2 das

3 shu

4 sin

cut : cutting fields
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With -f option you can cut the feilds delemited by some

character

$ cut -d" " -f1,4 students.txt

1 Mtech2 Btech

3 Mtech

-d option is used to specify the delimiter and -f option used

to specify the feild number

paste : pasting side by side
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paste command will paste the contents of the file side by

side

$ paste cutlist1.txt cutlist2.txt

1 Mtech 1 anil H12 Btech 2 dasgupta H4

3 Mtech 3 shukla H7

4 Mtech 4 singhvi H12

5 Btech 5 sumit H13

sort : ordering a file
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sort re-orders lines in ASCII collating sequences-

whitespaces first, then numerals, uppercase and finally

lowercase

you can sort the file based on a field by using -t and -koption.

$ sort -t" " -k 2 students.txt

/* sorts the file based on the second field

using the delimiter as space*/

grep : searching for a pattern
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grep scans its input for a pattern, and can display the

selected pattern, the line numbers or the filename where

the pattern occurs. usage: grep options pattern filename(s)

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Basic Linux comds -MIT.pdf